Musnad Ahmad 788:59

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Shaqiq, from Abu Musa, who said: A man came to the Prophet, may God bless him and grant him peace, and said: "O Messenger of God, what do you say about a man who fights out of bravery, and fights out of zeal, and fights for show? Which of those is in the way of God?" The Messenger of God, may God bless him and grant him peace, said: "Whoever fights so that the word of God, the Almighty and Majestic, is the highest, then he is in the way of God, the Almighty and Majestic."